Flowvis

Flowvis, the postprocessor for the CFD-code FLACS-CFD, is a program for visualising results from simulations of gas explosions, gas dispersion and multiphase flow.

Please see the section on Hardware and software requirements regarding the graphics card requirements for running Flowvis.

The current section gives a brief introduction to the main window of Flowvis. The main window is displayed all the time while Flowvis is running. The main window contains a menu bar, a tool bar, a properties sidebar, the plot area, and a time slider. If a presentation comprises several pages then these are accessed via tabs on the right of the plot area.

Figure 5.1: Flowvis main window

The menu bar contains the available menus.

The Flowvis tool bar is shown below.

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(a) (b) (c) (d) (e) (f)    (g) (h) (i)    (j)      (k) (I) (m) (n) (o) (p)    (q)

Figure 5.2: The Flowvis tool bar

Table 5.1: Tool bar buttons.

Button

Description

(a)

Creates a new presentation.

(b)

Opens an existing presentation.

(c)

Saves the presentation.

(d)

Deletes the selected plot, but puts it on the clipboard.

(e)

Copies the selected plot onto the clipboard.

(f)

Pastes a plot from the clipboard.

(g)

Creates a new page in the presentation.

(h)

Deletes the current page.

(i)

Sets the page layout: Several plots can be arranged in a grid on one page. Each plot can also span multiple cells of the grid.

(j)

Reloads the data from disk. Useful if a plot shows results from a running simulation.

(k)

Resets the current plot to the default view.

(l)

Returns to the previous view for the current plot (possible for zoom and pan operations in 1D and 2D plots).

(m)

Advances to the next view for the current plot (possible for zoom and pan operations in 1D and 2D plots).

(n)

Allows to move the plot region.

(o)

Enables to zoom in to the subsequently marked portion of the plot.

(p)

Opens the figure options dialogue.

(q)

Opens the Aggregation dialogue.

Right-clicking an empty area in the tool bar brings up a menu to hide or show the different tool bar sections, as well as the properties sidebar.

The properties sidebar shows the settings for the currently selected plot. The sidebar can be detached from the main window, or moved to a different location, by dragging it. Refer to the various plot types to see what properties can be set for each plot.

Note:

If you have closed the plot properties sidebar then you can get it back by right-clicking in the grey area of menu bar or tool bar. This will open the context menu where you can re-enable the plot properties entry.

Figure 5.3: The plot properties sidebar can be re-activated in the context menu available by right-clicking in the menu bar or tool bar.

The plot area can have multiple pages, and each page can contain multiple plots. Right-clicking in an empty space in the plot area shows the menu to create a new plot. A right-click on a plot shows the context menu for that plot. By clicking ”Set span” in the context menu, you can set how many cells in the plot layout the current plot will cover.

Figure 5.4: A presentation with four pages and a page layout with three plots.

Optionally, the top part of the plot area can be used to display a header for the current page. Using the headers can be switched on or off in the Options menu. The header will be visible on exported graphics.

Figure 5.5: The page header with information about the plots' origin and creation time.


The content of the page header can be changed per page or for all pages in the Page Settings dialogue box from the Page menu. Choose the Header page and fill in the desired text. In particular when assigning a text to all pages, the use of variables like the page number, the name of the presentation file, or the creation time can be useful. Flowvis will replace these variables by their value in the header on each page.

X

Page Settings

◎ Cancel

3 Apply

OkAII Pages

Figure 5.6: The Page Settings dialogue box allows to change the content of the page header.


The time slider has two modes that can be toggled by activating or deactivating Options →Synchronize Time. In synchronised mode (default), the time for all plots on a page is the same, the tick marks of the time slider are at the beginning values of the time steps, and clicking in the time slider selects a point in simulated time. When Synchronize Time is deactivated, the time slider selects time steps and the tick marks along the slider are equally spaced rather than according to the time step length. On a page with plots of different scenarios, the plots may then show different times, since a certain time step may refer to different times in the different datasets.

Figure 5.7: The time slider in synchronised mode (upper) and time step mode (lower). On the right, the drop-down menu that appears when holding down the play button is shown; here the animation speed can be reduced or increased.


An additional difference between the two modes of the time slider is that when playing an animation of the simulated time steps, Flowvis will aim to show the animation in real-time when Synchronize Time is

on. This means that simulations that cover a short time span (like explosions) will consist of only very few frames, depending on the speed of the computer used for visualisation. To play the animation at reduced speed (enabling the graphics card to produce more frames), left-click and hold the mouse pointer on the play button. In the drop-down menu that appears, choose one of the speed-up factors smaller than one.

If several plots are gathered in one presentation then these are accessed via tabs along the right hand side border of the plot area. The page names can be changed either per page or for all pages by specifying a template in the Page Settings dialogue box from the Page menu. The naming template may use variable text elements like the page number, the presentation file name, or the current date. Pages can also be dragged and dropped in the tab bar to rearrange their order.

Figure 5.8: The Page Settings dialogue box allows to change the names of pages as they occur on the tabs for page selection.

A Scalar Time plot is a curve plot where the value of one or several scalar variables is plotted over a time interval. Output from several simulations and for several monitor points can be combined in one plot.

Setting up a Scalar Time plot is quite straightforward, by selecting jobs, variables, and monitor points or panels for the selected plot.

Selecting jobs and variables can also be done via the context menu entry Data Selection. Other formatting options can be accessed by right-clicking into the plot or via the Edit menu. The axis ranges can be set in the Figure options dialogue.

In Flowvis, also 3D variables can be shown in Scalar Time plots. When selecting a 3D variable, the plot will contain a curve representing the median value of that variable, and a shaded area of the same colour that shows the whole range of values present at the corresponding time. The median and range are determined for the active region of the domain; the active region is set with the domain sliders in the properties sidebar. A similar range will be shown when using a 1D variable without selecting specific monitor points. In this case the minimum, maximum and median are determined based on the values from all monitor points.

Figure 5.10: Scalar Time plot with range and median shown over time for a selected part of the domain.

A scalar line plot is a 2D cartesian plot of a scalar variable, sampled along a straight line running through the simulation domain, for a specific time step. The line has to be parallel to one of the grid axes, but can be

positioned freely in the other two dimensions. In the properties sidebar for the Scalar Line plot, the scalar variable to plot can be selected in the Data Selection list. The placement and orientation of the line to sample values along, is specified by choosing which axis the line shall follow (X, Y or Z), setting the start and end position along this axis, and setting the position of the line in the other two axes.

The illustration below shows a Flowvis page with two sub-plots: a Scalar Line plot at the top, and a 2D Cut Plane at the bottom. A green dotted line drawn on top of the 2D Cut Plane illustrates the position of the sample line specified in the Scalar Line plot. The two plots are aligned in the horizontal direction (along the X-axis), as indicated by the four vertical red dotted lines drawn on top of both plots. The alignment of the two plots along the X-axis shows how the variations in scalar variable value (PROD 3D) along the line, matches in the two plots. Note that the green and red dotted lines in this figure is added on top of the Flowvis image using a graphics editor.

Figure 5.11: Scalar Line plot on top, showing data along the green dotted line in the 2D Cut Plane plot below.

The 2D cut plane plot type shows a two-dimensional cross-section of the domain or a part of the domain, parallel to a grid plane. The plot can include output for none, one or two variables. If two variables are combined, one must be a scalar variable and the other one must be a vector variable. Scalar variables are shown using filled contours while vector variables are displayed with arrows. The plot can include output from several simulations. The grid, geometry and porosities can also be included.

PROD (-)

Timestep/time: 4 / 407.46 ms Plane: XZ , 6 (3.57142m)

Figure 5.12: 2D cut plane plot

The plot has one legend for each variable. The legends are by default positioned to the right of the plot, but may be moved around freely by dragging them with the mouse. The colour map for each variable can be customised using the Appearance window in the properties sidebar.

The legend for vector variables includes arrow lengths. The arrow length is mapped to the vector magnitude in the 2D plane, while the colour is mapped to the magnitude in 3D space. This means that the colour of short arrows may indicate a high magnitude, because the vector may point into or out of the plane. The size and number of vector arrows can be adjusted using the Vectors option from the plot context menu.

Figure 5.13: 2D cut plane plot and controls in the properties sidebar.

In the Appearance dialogue in the context menu, the mapping of colours to data values can be specified for the active plot.

Figure 5.14: Colour map setup in the appearance dialogue.

Key elements of the colour map setup dialogue:

By enabling Verify Porosities in the Tools menu you switch on the porosity verification mode. When this mode is enabled, you will see an information box containing the porosity information for the cell the mouse cursor is positioned in. Note that the information is given as blockages rather than porosities. A value of 100% blockage means that no flow can pass through the surface or volume (0% porosity); a fully open passage has 0% blockage (100% porosity). The information comprises the volume blockage of the cell and the area blockages of the two faces perpendicular to each of the three coordinate directions.

The 3D plot type shows a three-dimensional representation of the geometry, together with simulation results. For scalar variables, four visualisation modes are available:

For vector-valued variables, the following visualisation modes are provided:

Warning:

The 3D plot should be used with caution, and not for extracting data values. Interpolation, numerical transformations, transparency settings, perspective distortion and graphical aliasing effects can lead to wrong values being observed. Use monitor points or panels, or the 2D cut plane plot to obtain more accurate values.

Figure 5.18: Different ways to visualise the velocity vector field; upper left: streamlines along a seeding line, integrated both backwards and forwards in time; upper right: same as before, but only integrated forward in time; lower left: streamlines seeded at random locations, lower right: glyphs/arrows.

A 3D plot can show many variables simultaneously, but there are limitations on the number of variables for a given visualisation mode: A maximum of two variables can be displayed as volumes. In addition, one variable can be shown per mode for the Surface, 2D slice, Glyphs and Streamlines modes. The Isosurface visualisation has no limitations.

Which variables are displayed in which way is prescribed when opening the data file or in the data selection window in the properties sidebar. Every data set has its own legend and settings and can be handled separately.

Figure 5.19: A 3D plot visualising several variables with the corresponding data selection status: PROD is shown as volume data (cloud), while the geometry surfaces are coloured according to the pressure P. The visualisation of the velocity vector field by streamlines is deactivated.

The check-box in front of each variable can be used to quickly enable/disable the visualisation of the variable. By right-clicking on the Unit field in the data lines, the unit used for creating the legend can be changed. Note that Flowvis will partition the legend at “nice” (e.g. integer) values in the current unit and this can lead to plots changing their appearance slightly when the unit is changed. In the Visualisation column, the intended visualisation mode can be chosen for each variable. The rightmost column allows to remove variables from the selection to free slots for other variables.

For the 3D plot type, the same kind of settings are accessible in the Appearance dialogue in the context menu as in the 2D plot appearance dialogue. If the activated variable is visualised using surface, 2D slices, glyphs or streamlines, additional options become available.

Table 5.2: Predefined color setups

Setup name

Description

Flame

Available for ”Temperature” variable. This setup uses additive color blending, and sets a value range and color table to give a flame like appearence.

Smoke

Available for ”MassFractionSoot” and ”VolumeFractionSoot” variables. This setup sets a dark color table, volumetric lighting and opacity settings to give a smoke like appearence. For the ”VolumeFractionSoot” variable, the opacity set will give a realistic viewing distance, corresponding to the Visibility output variable.

If the Manual radio button is active, the transparency curve can be manually drawn in the color map window using the mouse while holding down the left mouse button. If the Smoothstep radio button is active a smooth curve is computed for the defined min-max interval, going from a low to a high value (transparent to opaque).

In addition to the transparency curve in the color map, the overall transparency is controlled by the vertical slider to the right of the color map view. The value of this slider is multiplied with the value from the transparency curve, and makes it possible to easily set the general transparency level.

Fast Interpolation


Offset Interpolation

Volume porosity threshold

Figure 5.21: Appearance dialogue section for surfaces.

The Fast interpolation option applies only to 3D surface variables, not to volume variables. By default, the Fast interpolation option is disabled, which means that a more advanced interpolation algorithm for plotting surface values in the 3D plot is activated. The advanced algorithm takes into account porosities as well as grid alignment of the walls; in this way, the visualisation takes into account how the FLACS-CFD solver deals with such objects. The result is that the walls show more correct values on both sides. Currently, the advanced algorithm does not work for left difference primitives and it may fail on older graphics cards. Although the newer algorithm is robust and accurate, in a few rare cases (i.e. for walls aligned exactly with the center of a cell or sub-grid objects near walls) it might still show inaccurate results. It is therefore important to verify the 3D surface values against 2D cut plane plots and/or monitor points and panel values. When the Fast interpolation option is enabled, it does not take into account any porosities or the geometry position in the grid. Although slightly quicker, this can lead to wrong values being shown on the geometry.

Notably, thin walls will show the same value on both sides and the value will be an interpolation between the data on both sides of the wall. For instance, if there is a 2 bar overpressure on one side of the wall and 0 bar overpressure on the other side, the 3D surface plot may show the overpressure as being 1 bar on the wall. The Offset Interpolation option applies only to 3D surface visualization, i.e. projecting cell data onto object or terrain surfaces. If the surface of a large object (like a fuel storage tank) or terrain is cutting through a blocked cell with low porosity, the mapping of variable data on the surface can result in a suboptimal visual quality. E.g. on a curved or sloping surface the intersection may shift between blocked cells with no variable data, and (partly) open cells with variable data, resulting in a very irregular surface visualization. By enabling Offset Interpolation the interpolation algorithm will use variable data from the closest neighbour cell in the direction of the surface normal. The Volume porosity threshold slider / numeric field is used to adjust when the interpolation algorithm shall sample variable data from neighbour cell. The value represents the porosity value of the current intersected cell.

Figure 5.22: Appearance dialogue section for 2D slices.

Figure 5.23: Appearance dialogue section for glyphs.

For the seeding type Line, a magenta line segment can be positioned by moving the line's gray end points (green arrow) with the mouse while pressing the CTRL-key. To simplify positioning with the mouse, it is recommended to disable the perspective view and use axis-aligned view directions (red arrow). Alternatively, the exact coordinates of the end points can be defined using the controls available in the Appearance dialogue (red box). By clicking on the lock icons next to the axes names, the coordinates of the two end points are constrained to be the same along that axis. This facilitates the definition of axis aligned seeding lines. For instance, by ”locking” the Y and Z coordinates, the seeding line will be parallel to the X axis. The locking is ignored when dragging the end points with the mouse.

For the seeding type Random, the origins of the streamlines are distributed randomly in the domain.

It is possible to add several sets of streamline origins (Line or Random). This is particularly useful when several seeding lines are used to show the flow field in different parts of the domain. The parameters of each seeding line can be set individually by highlighting the it in the selection list at the top of the Streamlines dialogue.

Figure 5.25: Appearance dialogue section for volumes.


The accuracy of the volume rendering can be specified by using the slider.

Figure 5.26: The options window in the properties sidebar for a 3D plot.

Figure 5.27: Visualisation of the effects of ambient occlusion and edge enhancement.

In Flowvis, monitor points are coloured based on their validity given the scenario's geometry, grid and domain:

– Cell volume blockage is greater than 90%.

– All the cell faces have a porosity blockage greater than 50%.

– The monitor point is placed outside the domain.

Note:

The colouring of monitor points is not functional when using CGNS files.

Two of the panel types, hinged rigid and popout rigid, has additional visualization features. The position of the popout rigid panel will move when the panel yields, illustrating the ”popout”-functionality. The hinged rigid panel will indicate the hinge side of the panel using a solid yellow cylinder, and the panels representation will also swing open like a hinged door when the panel yields.

Figure 5.28: Comparing the visualization of the popout-rigid (Panel2), popout(Panel3), hinged-rigid (Panel4) and hinged (Panel 5), before (left image) and after (right image) the panels yield.

d* cad_geo1.fvp - Flowvis 5.8.0 - FLAGS v10.7r1                                                                                                —     □ X

File Edit Page Plot Tools Options Help

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3D Plot Properties


旧 Grayscale Geometry

0 Show Geometry

I I Shadows □ Sky



□ 0



Ignition location

CAD Model


Show description


□



Light position


South East



Figure 5.29: The original CAD model shown in Flowvis.

Figure 5.30: Setting the light position.

Figure 5.31: Example of concrete ground displayed under a geometry.

Note:

In case there is a ground object in the FLACS-CFD geometry, it is recommended to add a small vertical offset (e.g. +0.05m) to the ground height defined in Flowvis to avoid or reduce rendering artefacts. Alternatively you can apply transparency to the ground object.

The geometry window allows to change the appearance of the geometry objects in 3D plots. Such changes are based on the hue value assigned in CASD or when importing the geometry. Based on the hue, objects can be displayed with a different colour, as mapped by a colour map, and they can be made partially transparent.

Figure 5.32: Different settings for the geometry visualisation. The Geometry window for the each subplot is shown side by side with the plot. Top left: standard settings, no transparency and the objects' hue values are directly used as colours; top right: a different colour map has been applied; lower left: the outer walls have been made transparent, the other geometry is fully opaque; lower right: all objects are partly transparent.

To be able to easily make, for example, the outer walls transparent, these parts of the geometry have to be assigned a hue value of their own. Transparency is a powerful tool to visualise solution values, for example a gas cloud, along with the relevant geometry. On complex geometries, however, the use of transparency is, computationally demanding and the performance of Flowvis can degrade.

When very many monitor points or panels are defined in a FLACS-CFD scenario, it may be overwhelming to show them all in a 3D plot. On the other hand, one often wants to illustrate where in space certain measurements, e.g. pressure-time curves shown in a separate plot, are taken. This is possible by defining the monitors that are to be shown as a group, or with a distinct name prefix, in CASD. By right-clicking in the 3D plot and choosing Monitor selection you open a window with the list of monitors defined for the scenario. You can either filter the list by a string, which is useful if you have given the monitors to be shown a common name prefix, or alternatively select the monitors to be shown with the mouse; the latter also works easily with groups of monitors as defined in CASD.

Filter

虱卡雄金I

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Monitor Selection:

Position

Cancel

<100.5, 90.5, 26.5> m

<100.5, 94.5, 26.5> m

<100.5, 98.5, 26.5> m

<1005 1025 26.5>...

<1005 106.5, 26.5>...

<100.5, 110.5, 26.5>...

lowerDeck [32]

MP 1

MP4

MP 7

MP 10

MP 13

MP 16

k

Name

Figure 5.33: By selecting the lowerDeck group, only monitors on the lower deck are shown in the 3D plot.


5.3.4.7 Flight mode


Flowvis has an experimental facility to define sequences of viewpoints so that movies can be created in which the camera moves around the geometry as time advances. Flight mode is enabled by clicking the airplane logo in the icon bar of a 3D plot window. This will open the flight path editor.

PROBIT

flight path

4.2e+08

2.9e+08

8.3e+07

view points and • direction vectors

~| Position

Direction

]Direction [ 0.26,-0.94j0.24

-10.88,-31.51,... 0.55, 0.83,-0.04 20.34, -53.96,... -0.09,0.99, -0.15 55.60, 7.34, 9.91 -0.99, 0.00, 0.12

I Run: 600001

Var: PROBIT 3D

Time: 19973.33 ms (4)

Figure 5.34: Flowvis in flight mode with a defined flight path.



To define a flight path, follow these steps:

While the flight path editor is open, the flight path is shown by a green line with gray dots at the defining positions. The flight path can be modified by dragging the gray dots with the mouse while holding down the CTRL key. Alternatively, you can double-click a view point to jump to it, change the view as desired, and then click Add to update the view point.

This visualisation of the flight path is hidden when the flight path editor is closed. Note that closing the flight path editor does not leave flight mode, so that it is possible to show and export the flight sequence without the flight path being visible. The solution variable(s) shown will also update according to the defined time. When flight mode is deactivated in the icon bar, the view point is set to the current one and hitting the play button will only make the solution advance, without camera movement. The flight path for a 3D plot is saved in the Flowvis presentation file and recalled when re-entering flight mode.

PORX_3 口

PORY_3D

Filter variables wraps existing variables and applies a function on the data before returning it. They can be used to calculate, for example, the moving average of a specified variable. The filter variable menu can be found in the context menu of the variables in the Data Selection section.

After selecting a filter it will prompt you for the necessary input required to make it, and then a new variable will be created with the provided name. This new filter variable can now be used as any other variable in the presentation. The Moving Average filter calculates the moving average of a variable over a specified window. The window specified is in seconds and ends at the current timestep. The Maximum over time filter can be used to propagate the maximum value in the cells over time, and the Maximum over axis filter can be used to propagate the maximum value in the cells in the specified direction.

Note:

The ”Maximum over axis” filter is only applicable to 3D variables.

Shortcut: CTRL-E

The File → Export Graphics menu item opens a dialogue that allows to save pages and presentations as pixel graphics (file formats: png, jpg, tif) or vector graphics (file formats: svg, eps, pdf). The file format can be changed by clicking on Browse or by manually changing the extension of the filename.

If multiple pages or time steps are selected for export, Flowvis will put these into a single file if the file format permits that, or alternatively into several files using counters in the file name (%P or %T for pages and time steps, respectively).

When exporting as a pdf document, all time steps for a given page are placed in the same file. Therefore, using the %T counter with pdf documents does not result in multiple documents.

The Specified timesteps option is only available when time is not synchronized. Vice versa, the Time range option is only available when time is synchronized.

Figure 5.36: The Export graphics dialogue allows to save pages and presentations as pixel or vector graphics.

If the file format is set to tif, Flowvis will generate a georeferenced image file (GeoTIFF) by including relevant coordinate transformations within the image file. The GeoTIFF parameters group in the Export Graphics GUI will be enabled if the output filename ends with ”.tif”, and can be used to place the exported image in the correct location when imported into a GIS system. The X and Y offset parameters in the export dialog will be added to the position in the FLACS-CFD coordinate system. If the geometry has been rotated in CASD e.g. in order to align the orientation of objects with the coordinate axis, the Rotate GeoTIFF parameter can be used to correct for this rotation in the export, by applying a negative rotation of the same amount. Values for Offset and Rotation will be initialized using information read from the geometry (.geo) file.

GeoTIFF file export works best with 2D cut plane plots that are oriented in the XY plane. In order to export GeoTIFF files from a 3D plot, the view orientation has to be top-down (use the View Along Z/-Z axis button in the lower right), and the view has to be orthographic (use the Perspective camera icon/button in the lower right).

By checking the the Do batch export option and selecting a number of similar scenarios before clicking on the OK button, all the selected scenarios will be exported using the same settings (e.g. view point, time-step, resolution, etc.)

Note:

When using the batch export option all the selected scenarios should have similar properties.

Shortcut: CTRL-SHIFT-E

The File → Export movie menu item opens a dialogue that allows to save pages as movies (file formats: AVI, wmv, MPEG, MPEG4). The export format can be changed by clicking on Browse.

The Time range option is only available when time is synchronized. The viewpoint and view direction during movie export can be animated using the flight mode feature.

If you want to export movies of multiple similar scenarios using the same settings, the batch export functionality can be used, in the same way as described for exporting graphics.

Figure 5.37: The Export movie dialogue allows to save pages as movies.

If the option 360 video export is checked, a 360 degree video (using equirectangular projection) will be created from the current camera position.

Figure 5.38: Example of a frame from a 360 degree video export. When played in a viewer that support 360 videos, the user can interactively look around while viewing the video.

Shortcut: CTRL-ALT-E

The File → Export 360 FOV Graphics menu item opens a dialogue that allows the user to export all pages or the current page to 6 images per page that can be converted to a 360° view using tools such as Marzipano. Each page are exported using the page name postfixed with a single letter representing the camera direction.

Figure 5.39: The Export 360 FOV Graphics dialogue.

When exporting 360° views the width and height resolution must be the same. This is ensured by locking the two input fields such that it is not possible to enter different values.

Since the purpose of this export type is to generate a 360° view any 2D object in the plot, such as the FLACS-CFD logo overlay, legend or any text box, should only be visible in 1 of the 6 images that are

exported. To facilitate this the export dialogue allows the user to choose in which direction any 2D items should be visible with the Legend direction option.

The formatting of decimal numbers in the legends in Flowvis can be changed in the settings accessible via the Options menu, selecting Preferences. The number of decimal or significant digits can be set and either scientific or standard notation selected.

TDOSE 3D (mg/m3*minute) -   ^^5.8438e+09


TDOSE 3D (mg/m3*minute)


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2.6667e+09


1.3333e+09


0.0000


2.66667e+09


1.33333e+09


0.00000


2666666666.66667


1333333333.33333


0.00000


Number precision: [ 5 用 | Significant digits

Use scientific notation:区|


Number precision: [ 5    :，| Decimal places

Use scientific notation:区|


Number precision: [ 5 圉 | Decimal places Use scientific notation: U


Figure 5.40: Different number format settings and how they affect a sample legend.

Flowvis will display the terrain in both 2D cut plane plots and 3D plots. You can enable/disable showing the terrain using the Terrain checkbox in the plot context menu (right click on the plot). In a 2D cut plane plot, the terrain intersection is drawn as brown dashed line in XZ and YZ planes. In XY planes, brown hachure indicates the areas where the current cut plane is located under the terrain.

Figure 5.41: Visualisation of terrain in 2D plots with different cut planes and a 3D plot.


Note:

When using large terrains in Flowvis, the parts that are far away (more than ca. 10 km) from the view point may be clipped. The same clipping (far plane culling) applies to other geometry as well. Zooming in or changing the view angle may help to show the entire geometry, but the best way to avoid the effect is to restrict the range of the terrain during the terrain import in CASD.

Plot linking allows you to connect two or more plots such that they share certain properties. The set of properties that can be linked depends on the plot types that are linked: each plot type has a set of linkable properties and it will only be possible to link the properties that are common to all linked plots. The following properties can be linked:

Table 5.3: Linkable plot properties.

Property

Description

Applicable plot types

Variables

selected variables

all

Plot domain X

domain of the plot in the X-direction

2D cutplane plot, 3D plot

Plot domain Y

domain of the plot in the Y-direction

2D cutplane plot, 3D plot

Plot domain Z

domain of the plot in the Z-direction

2D cutplane plot, 3D plot

Plot domain horizontal

horizontal plot domain (current X and Y axis)

scalar time plot

Plot domain vertical

vertical plot domain

scalar time plot

Data files

simulations forming the basis for the plots

all

Colormap settings

range, subdivision and palette of the colormap. These settings can be found in the Appearance menu.

2D cutplane plot, 3D plot

3D view

view position and angle, zoom

3D plot

A link can be created by holding the CTRL key down while selecting two or more plots with the left mouse button. After multiple plots have been selected, they are linked by right clicking on one of the highlighted plots and selecting Create link. This will automatically open the Link properties window in the Properties sidebar as described in The properties sidebar. Links can also be created and deleted directly from the Link properties window. In the case that this window is closed, it can be opened by following the instructions in The properties sidebar.

Note:

Only plots on the same page can be linked. A plot can only be part of one link at a time.

Figure 5.42: A link of the 3D view property has been created between the four 3D plots. This ensures that the view settings are always the same for all four plots.





The legend of one or several plots can be placed to the right of the plots in a sidebar. There are several use cases for this, the most common ones are:

The legend for a plot can be placed in the sidebar by right clicking on the plot and selecting Show legend in sidebar. The sidebar legend window can be resized horizontally by dragging the gray line between the plots and the right sidebar.

When placing a legend in the sidebar to avoid legend duplication, it may be necessary to disable the legend on other plots. For the 3D plot and 2D cutplane plot the legend can be disabled in the Appearance menu in the plot properties sidebar. For scalar time and scalar line plots, the legend can be disabled from the context menu under Legend location.


Figure 5.43: A page with four plots and the legends placed in the sidebar.



The two plots shown in figure above have identical legends. One of the legends can be placed in the sidebar

by right clicking and choosing Show legend in sidebar. In this example the legend for the upper plot is placed in the sidebar. The legend for the lower plot can then be hidden by unchecking the Show legend option under Appearance in the properties sidebar.

Figure 5.45: The same page as before but with the legend placed in the sidebar.

The aggregation dialogue is opened by clicking on the corresponding button in the Flowvis tool bar:

Figure 5.46: The Aggregation button (red frame) in the Flowvis tool bar.

In some cases it can be beneficial to aggregate results from multiple runs into a single result. For example, you may want to show the maximum overpressure from several explosion simulations as a single 3D field. This can be accomplished by using the Aggregation functionality in Flowvis.

The aggregation function always aggregates across time and runs.

Figure 5.47: The aggregation dialogue with basic settings.

Figure 5.48: The aggregation dialogue with advanced settings.

There are a number of different options available in the aggregation dialogue. By default only the most common options are shown. All options can be shown by clicking on ”Advanced settings”. See below for an overview of the different options available in the aggregation dialogue.

Table 5.4: Aggregation options

Option

Description

Runs

This field lists the runs which can be aggregated. Multiple runs are selected by holding down the CTRL-key and left-clicking the job numbers.

Option

Description

Variables

Here you can select the variable to aggregate. It is only possible to aggregate one variable at a time. All variables that exist in at least one run are displayed.

Aggregation type

The type of aggregation to perform.

Save directory

The directory where the aggregated results should be saved.

Save file name/jobnumber

Job number to assign to the aggregated data when saving it. The standard FLACS-CFD job number format applies here.

Resample to grid

The aggregation algorithm calculates results on a single grid. This can be the same grid as one of the simulations or completely different. In most cases the results from one or more simulations will need to be resampled to fit this grid. By default the grid of the first simulation is used. In many cases, especially for dispersion simulations, it will be desirable to use a course or more uniform grid for the aggregation.

Open when finished

When enabled, the aggregated results will be opened in the chosen plot type when finished.

Custom title

Custom title used in the generated cs-file.

Custom description

Custom description used in the generated cs-file.

Behaviour if grid is different

If the selected runs have different grids, you can choose between three courses of action: resampling to a base grid, skipping the simulation, or stopping the aggregation. In most cases resampling to a base grid is the best choice.

Timesteps

Allows you to specify whether the aggregation should be applied to all timesteps or only to the last timestep. The latter can be useful when aggregating variables such as PMAX.

Propagate boundary values

When this option is enabled and the grid that the results are resampled to are larger than the original grid for a given run, the boundary values of that run will be propagated/extended outside of the original grid dimensions. This is the conservative and safe option, but may produce artifacts if any of the border values are significant.

Outside boundary value

This field is only editable when Propagate boundary values is disabled. Allows you to manually specify what value should be assigned to the cells outside the original grid dimensions.

The following example demonstrates the aggregation functionality for a simple case where the maximum pressure PMAX is maximised over the results from four scenarios. The runs are based on example 4 from the FLACS-CFD course. Since the PMAX field contains the maximum pressure that has occurred per grid cell in the course of a simulation, it is sufficient to aggregate over the last time step from each of the four simulations.

Figure 5.49: The settings applied in the Aggregation dialogue for the example with four different scenarios.

Figure 5.50: The PMAX result for each of the four scenarios individually.

Figure 5.51: The aggregated PMAX result, showing in each point the maximum pressure that has occurred in one of the four runs.

The current section gives an idea of some deficiencies and the future development of Flowvis, and should help to avoid communication and feedback regarding issues that are already known. If you find other issues, limitations or bugs please contact flacs@gexcon.com and help us to improve Flowvis and make in the way you want it to be!

For pages with several plots the following settings in the Options menu may help to work efficiently and obtain optimal results:

Synchronize Time (default)

Display seconds changes the time unit displayed in the plot from milliseconds to seconds; this is recommended especially for longer simulations such as dispersion and fire scenarios

Flowvis will write messages regarding warnings and errors to the console if needed. The detail level of the output can be changed using the -v or --verbose commandline parameter, or by setting the FLOWVIS LOG LEVEL environment variable. Starting Flowvis with -v will increase the log level to include info messages. Starting Flowvis with -vv or -v -v (repeating it two times), will increase the log level to include both info and debug messages. The same functionality can be achieved by setting the FLOWVIS LOG LEVEL environment variable to 1 or 2.

It is also possible to make Flowvis create a log file. In order to trigger the generation of a log file, use the commandline parameter -l or --logfile, followed by the full path to the logfile, e.g.

> flowvis.exe -l C:/tmp/flowvis-log.txt

An alternative way to create a log file is to set the environment variable FLOWVIS_LOG FILE to a file path. Please note that the directory in the path must exist or Flowvis will generate an error message and fail to start.

FLACS-CFD v22.2 User’s Manual

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